The present invention relates to a lubricating device for a valve driving mechanism of an engine.
Lubricating slide portions located between a cam shaft and a journal bearing or between a cam portion and a rocker arm or a valve lifter may be required for a valve driving mechanism. Japanese Patent Laid-Open Publication No. 2001-329823, for example, discloses a lubricating device for the driving mechanism, in which at an inner-wall ceiling face of a cylinder head cover (rocker cover) is provided an oil guide portion which collects lubricating oil spread by a chain transmitting an output of a crank shat of a single-cylinder engine to a cam shaft and guides the collected lubricating oil to the valve driving mechanism. It may be difficult to guide the lubricating oil to a specified portion which is located away from the chain according to the above-described lubricating device. Thus, this lubricating device may not be properly applied to a valve driving mechanism for a multi-cylinder engine.
Meanwhile, a lubricating device for the multi-cylinder engine, which comprises an oil passage of lubricating oil formed inside a cam shaft and a nozzle which is provided so as to open at a peripheral surface of a shaft portion of the cam shaft or a cam portion and connect to the oil passage formed inside the cam shaft, has been put to practical use. This lubricating device may enable a proper lubricating of respective slide portions.
Herein, in a case in which the lubricating oil is ejected out of the nozzle opening at the peripheral surface of the cam shaft and the slide portion, such as the peripheral surface of the cam portion and the rocker arm, are lubricated by the lubricating oil ejected, there may occur two states: a state in which the nozzle is directed to the slide portion; another state in which the nozzle is not directed to the slide portion, in accordance with the position change of the cam portion caused by the rotation of the cam shaft. Although the lubricating oil is supplied to the slide portions while the cam shaft is so positioned that the nozzle is directed to the slide portion, the supply of the lubricating oil to the slide portion is not conducted when the cam shaft is so positioned that the nozzle is not directed to the slide portion. Therefore, the lubricating oil ejected out of the nozzle would be ejected wastefully into a vale-driving chamber. Further, as the number of intake/exhaust valves increases, the number of nozzles also increases accordingly. Thus, the amount of such wasteful lubricating oil ejected would increase. The increase of the amount of lubricating oil may increase the burden of a pump to supply the lubricating oil. Since the pump is generally driven by the engine, such increase of the amount of lubricating oil may cause the increase of the burden of the engine. As a result, the fuel economy of the engine would deteriorate.